We examine the role of baroclinic instability in transferring thermal gradients from the surface of the ocean to the abyss, and thus determine the stratification. The hypothesis is that the density differences imposed at the surface by differential insolation are a large source of available potential energy which can be released by mesocale eddies with horizontal scales of the order of 10 km. This process deepens the region of horizontal gradients (i.e. the thermocline). This process is analyzed in the context of a rapidly rotating primitive-equation flow driven by specified surface temperature, with diffusion and friction.

This conjecture is in contrast with the current thinking that the deep stratification is determined by a balance of turbulence at smaller scales and the large-scale ocean circulation.